Why change it to xp? I installed vista home premium on a 3 year old hp laptop. It has yet to have a problem.It does not start as fast or shutdown as fast but then I put it into sleep and it only takes a few seconds to start back up. I have some people in my office here(we do computer support for a private college) and they will not go back to xp as it offers no real advantage over vista. Vista got a bad rap as when it first came out, people tried to put it on computers that really could not support it. What you need to do is get rid of the install that dell does. Format the thing and reinstall vista from scratch.
THEN you put on what you want and not all the extra crap the pc vendors throw on.
I have a toshiba that is a little over a year old. it has ONE gig of ram, it runs vista fine. Funny how some many people talk bad about vista when it works good. It IS just as stable now as xp is. With a proper pc, it is virtually as fast in operation. It IS most resistant to viruses AND is much more secure than xp ever was.
What is also funny is that these same issues happened with xp when it first came out but how quickly people forget.
Get the disk with the pc. Format it and reinstall vista(another area which is MUCH better than xp, raid drivers anyone?),
install what you want and I bet it will work just fine. I will say to make sure you install service pack 1. It helps a lot, unlike service pack 2 and 3 for xp which broke things at first.
As an aside, I run 10 year old software just fine on vista. The video card in my hp laptop has no vista drivers from intel, yet vista supports it great. Vista is light years ahead of xp in terms of driver support now. When it first came out, that may not have been the case but it is true now.